Phosphorus oxychloride preparation method based on flat-plate membrane reactor

Abstract

The invention discloses a phosphorus oxychloride preparation method based on a flat-plate membrane reactor, and belongs to the technical field of chemical processes and reactors. The reactor comprises a plurality of liquid chamber-gas chamber-liquid chamber functional units which are arranged repeatedly and heat exchange units located between the adjacent functional units, gas-liquid micro-interface contact is achieved through a porous hydrophobic membrane, and oxygen reacts with phosphorus trichloride in a molecular diffusion mode. According to the method, the reaction temperature is controlled to be 70-95 DEG C, the oxygen pressure is controlled to be 0.01-0.05 MPa, and the heat exchange medium is combined for circulating heat transfer, so that efficient utilization of oxygen is realized, and the reaction process is mild and controllable. The continuous operation of 3-5 reactors connected in series is supported, the oxygen utilization rate can be remarkably improved, the raw material consumption is reduced, the product purity is improved, continuous production is supported, and the method is suitable for large-scale synthesis of phosphorus oxychloride.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering and process technology, specifically relating to a novel preparation method and reactor for chemical products, and particularly to a flat-plate membrane reactor with an integrated heat exchange unit and its application in the preparation of phosphorus oxychloride. Background Technology

[0002] Phosphorus oxychloride (POCl3), a key chemical intermediate, is traditionally prepared using a batch reactor, where oxygen is bubbled into a liquid layer of phosphorus trichloride (PCl3) to carry out the reaction. This process suffers from two fundamental, interconnected defects in reaction engineering: low oxygen utilization and limited gas-liquid mass transfer interface area, which directly restricts reaction efficiency and economics.

[0003] In traditional bubbling reactions, oxygen passes through the liquid reactants in the form of bubbles. Most of the oxygen fails to dissolve and diffuse sufficiently in the liquid phase before escaping from the surface to the top space, forming oxygen-rich exhaust gases. This results in significant waste of reactants (O2) and increased raw material consumption. Achieving precise delivery and efficient utilization of oxygen molecules, while avoiding their ineffective dissipation, is a core problem urgently needing to be solved in this field.

[0004] While some improvements have been attempted in existing technologies, none have fundamentally solved the aforementioned core problems. For example, utility model patent CN207709053U discloses a "phosphorus oxychloride membrane-type oxygenation reactor." This solution mainly uses a liftable jet pipe to prevent the pipe from being immersed in liquid for extended periods, thus extending the equipment's lifespan, and includes an external detection sleeve to indicate leaks in the reactor. However, the so-called "membrane-type" does not refer to a functional membrane for achieving gas-liquid micro-interface mass transfer; its reaction mechanism is essentially still macroscopic bubble bubbling oxidation. Therefore, it cannot improve the dispersion and effective utilization of oxygen in the liquid phase, nor can it provide a stable, large gas-liquid mass transfer interface to increase the reaction rate. Its technical focus is on the mechanical protection of the equipment and leak monitoring, rather than the enhancement of the reaction process.

[0005] Therefore, there is an urgent need in this field for a novel reaction technology that can precisely control oxygen transfer and provide a stable and efficient mass transfer interface, so as to fundamentally improve the economy and safety of the phosphorus oxychloride synthesis process. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing phosphorus oxychloride based on a flat-plate membrane reactor. This method utilizes a gas-liquid contact mechanism that is fundamentally different from existing technologies, aiming to achieve efficient utilization of oxygen, precise control of the reaction process, and continuous production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A flat-plate membrane reactor includes a rigid frame and multiple functional units disposed therein, as well as heat exchange units between adjacent functional units. Each functional unit is a liquid-gas-liquid chamber formed by membrane assembly. The heat exchange units are heat exchange chambers located between adjacent liquid chambers of adjacent functional units or between liquid chambers and the rigid frame, which are separated by thermally conductive partitions. The diaphragm assembly and the thermally conductive baffle are fixed to the rigid frame by sealing strips to ensure complete isolation of each chamber; The reactor is equipped with end caps at both ends, and the end caps are respectively equipped with a circulating medium inlet, an oxygen inlet, a phosphorus trichloride inlet, a liquid outlet, a gas outlet, and a circulating medium outlet. The circulating medium inlet and the circulating medium outlet are connected to the heat exchange chamber and are respectively connected to the circulating medium supply device and the circulating medium treatment device. The oxygen inlet and the gas outlet are connected to the gas chamber and are connected to the oxygen supply system and the tail gas treatment system. The phosphorus trichloride inlet and the liquid outlet are connected to the liquid chamber and are connected to the phosphorus trichloride conveying pipeline and the product outlet pipeline. The end cap is also provided with a pressure detection port and a temperature detection port, which are connected to a pressure sensor and a temperature sensor, respectively, to detect the reaction pressure and reaction temperature inside the reactor.

[0008] The flat-plate membrane reactor used in this invention is a highly integrated modular reaction device. Its core structure consists of multiple sets of repeating functional units and heat exchange units between these units. The functional units adopt a "liquid chamber-gas chamber-liquid chamber" configuration, with membrane components serving as the separating interfaces. Oxygen flows within the gas chambers and diffuses through the membrane pores. The liquid chambers are adjacent to the gas chambers, supplying a mixture of phosphorus trichloride and phosphorus oxychloride, where an oxidation reaction occurs at the membrane interface. The heat exchange chamber is located between two liquid chambers, directly contacting both sides of the liquid chambers via a thermally conductive partition. The heat exchange medium circulates within a closed channel, enabling bidirectional and immediate removal of the heat of reaction. This design ensures that each gas chamber has liquid chambers on both sides for reaction, and each heat exchange chamber has liquid chambers on both sides for heat exchange, forming a more efficient heat management and reaction system.

[0009] Furthermore, the functional units and heat exchange units are arranged in parallel within a rigid frame, which is made of corrosion-resistant materials such as polyvinylidene fluoride (PVDF), stainless steel, or titanium alloy.

[0010] Furthermore, the number of the functional units is 4-20.

[0011] Furthermore, the sealing strip is made of one of the following materials: polyvinylidene fluoride, polypropylene, polyvinyl chloride, plexiglass, silicone rubber, fluororubber, and ethylene propylene rubber.

[0012] Furthermore, the membrane assembly is composed of a porous hydrophobic membrane and a support layer. The porous hydrophobic membrane has a thickness of 80-200 nm and a pore size of 0.1-1.0 nm, allowing only gaseous oxygen molecules to penetrate through the "dissolution-diffusion" mechanism. The support layer has a thickness of 100-300 μm and has a porous mesh structure, which can provide reliable mechanical support for the surface layer.

[0013] Furthermore, the specific surface area of ​​the porous hydrophobic membrane is 1500-3000 m². 2 / m 3 Preferably 2000-2500 m 2 / m 3 The oxygen permeability is 0.1-10 L / min / cm. 2 .

[0014] Furthermore, the material of the porous hydrophobic membrane is one or a copolymer of polytetramethylpentene, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene, polysulfone, polyethersulfone, silicone resin, and polydimethylsiloxane.

[0015] Furthermore, the material of the support layer is selected from either polyester nonwoven fabric or polypropylene nonwoven fabric.

[0016] Furthermore, the heat exchange chamber is a plate heat exchange structure, and the internal circulating medium can be flexibly selected according to the in-situ temperature control requirements, preferably heat transfer oil or circulating cooling water.

[0017] Furthermore, the heat-conducting partition of the heat exchange chamber is selected from one of 316 / 316L stainless steel, duplex stainless steel, industrial pure titanium, Hastelloy, or Inconel; or graphite or silicon carbide ceramic materials can be used.

[0018] A method for preparing phosphorus oxychloride based on a flat-plate membrane reactor, wherein the method uses phosphorus trichloride and oxygen as raw materials and carries out an oxidation reaction in a flat-plate membrane reactor, including the following steps: Phosphorus trichloride is continuously introduced into the liquid chamber of the reactor, while oxygen is introduced into the gas chamber to control the reaction temperature and oxygen pressure. Oxygen permeates through the micropores of a porous hydrophobic membrane under pressure, and the micro-interface contact between the gas and liquid phases is achieved through the porous hydrophobic membrane, allowing oxygen to undergo an oxidation reaction with phosphorus trichloride in the form of molecular diffusion to generate phosphorus oxychloride. During the reaction, the heat of reaction is removed in a timely manner through the circulation of the heat exchange medium to maintain a stable reaction temperature; the reaction products are continuously discharged from the liquid chamber outlet.

[0019] Furthermore, the phosphorus trichloride feedstock is continuously pumped from the upstream feed tank into the liquid chamber of the flat-plate membrane reactor via a transfer pump, and the phosphorus oxychloride-rich product generated by the reaction is continuously discharged from the liquid chamber outlet and enters the downstream product collection or purification unit. The entire process is a unidirectional continuous flow.

[0020] Furthermore, the molar ratio of phosphorus trichloride to oxygen is 2:1-3.

[0021] Furthermore, the reaction temperature is 70-95℃, preferably 85-95℃.

[0022] Furthermore, the oxygen pressure is controlled within the range of 0.01-0.05 MPa.

[0023] Furthermore, to improve the single-pass conversion rate and system capacity of phosphorus trichloride, multiple reactors are connected in series, with the number of reactors in series being 3 to 5.

[0024] Furthermore, when multiple reactors are connected in series, the inlet of the liquid chamber of the first-stage reactor is connected to the phosphorus trichloride delivery pipeline, and its liquid chamber outlet is connected to the inlet of the liquid chamber of the second-stage reactor. The liquid chamber outlet of the second-stage reactor is then connected to the inlet of the liquid chamber of the third-stage reactor, and so on. Each stage of the reactor is equipped with a separate gas and circulating medium supply system and treatment system.

[0025] Furthermore, the phosphorus oxychloride product obtained by the preparation method has a purity of ≥99.0% and an unreacted phosphorus trichloride content of ≤0.3%.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High oxygen utilization and low raw material consumption: The gas-liquid interface is achieved through the membrane module (porous hydrophobic membrane). Oxygen diffuses through the membrane pores and reacts with phosphorus trichloride, which greatly improves the mass transfer efficiency and effectively reduces raw material consumption and exhaust gas treatment costs.

[0027] 2. The reaction process is mild and controllable, resulting in excellent product quality: The membrane interface reaction mechanism avoids the local overheating phenomenon in traditional bubbling reactions. Combined with the precise temperature control (70-95℃) of the integrated heat exchange unit, the occurrence of side reactions is effectively suppressed. The purity of the obtained phosphorus oxychloride product can reach over 99.0%, and the product is colorless and transparent.

[0028] 3. Simple process flow, easy to implement continuous production: The process adopts a unidirectional continuous flow process, which eliminates the need for material recirculation and simplifies process control; by connecting multiple membrane reactors in series, the production capacity and conversion rate can be flexibly adjusted to meet the production needs of different scales. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the flat-plate membrane reactor of the present invention.

[0030] In the diagram: 1. Circulating medium inlet; 2. Oxygen inlet; 3. Phosphorus trichloride inlet; 4. Heat exchange chamber; 5. First liquid chamber; 6. Gas chamber; 7. Second liquid chamber; 8. Heat exchange chamber; 9. Liquid outlet; 10. Gas outlet; 11. Circulating medium outlet. Detailed Implementation

[0031] The technical solution and effects of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0032] like Figure 1 As shown, this embodiment provides a flat-plate membrane reactor. The reactor is a closed rectangular pressure-bearing structure, including a rigid frame and multiple functional units disposed therein, as well as heat exchange units between adjacent functional units. Each functional unit is a liquid-gas-liquid chamber formed by membrane components. The heat exchange units are heat exchange chambers located between adjacent liquid chambers of adjacent functional units, or between liquid chambers and the rigid frame, separated by thermally conductive partitions. Specifically, as shown... Figure 1 As shown, the reactor is arranged in the following order: heat exchange chamber 4, first liquid chamber 5, gas chamber 6, second liquid chamber 7, heat exchange chamber 8, third liquid chamber, gas chamber, and fourth liquid chamber. The diaphragm assembly and the thermally conductive baffle are fixed to the rigid frame by sealing strips to ensure complete isolation of each chamber; The reactor is equipped with end caps at both ends. The end caps are respectively equipped with a circulating medium inlet 1, an oxygen inlet 2, a phosphorus trichloride inlet 3, a liquid outlet 9, a gas outlet 10, and a circulating medium outlet 11. The circulating medium inlet 1 and the circulating medium outlet 11 are connected to the heat exchange chamber 7 and are respectively connected to the circulating medium supply device and the circulating medium treatment device. The oxygen inlet 2 and the gas outlet 10 are connected to the gas chamber and are connected to the oxygen supply system and the tail gas treatment system. The phosphorus trichloride inlet 3 and the liquid outlet 9 are connected to the liquid chamber and are connected to the phosphorus trichloride conveying pipeline and the product outlet pipeline. The end cap is also provided with a pressure detection port and a temperature detection port, which are respectively connected to a pressure sensor and a temperature sensor to detect the reaction pressure and reaction temperature inside the reactor.

[0033] In this embodiment, the functional units and heat exchange units are arranged in parallel within a rigid frame. The rigid frame and sealing strips are made of corrosion-resistant stainless steel. The sealing strips are used to fix the diaphragm assembly and the heat-conducting partition within the frame to ensure complete isolation of each chamber.

[0034] In this embodiment, the reactor contains 4 functional units and 5 heat exchange units.

[0035] The membrane assembly in this embodiment is composed of a porous hydrophobic membrane and a support layer. The porous hydrophobic membrane has a thickness of 80-200 nm and a pore size of 0.1-1.0 nm, allowing only gaseous oxygen molecules to penetrate through the "dissolution-diffusion" mechanism. The support layer has a thickness of 100-300 μm and has a porous mesh structure, which can provide reliable mechanical support for the surface layer.

[0036] Furthermore, the specific surface area of ​​the porous hydrophobic membrane is 1500-3000 m². 2 / m 3 Preferably 2000-2500 m 2 / m 3 The oxygen permeability is 0.1-10 L / min / cm. 2 .

[0037] In this embodiment, the porous hydrophobic membrane is made of polytetrafluoroethylene, and the support layer is made of polyester nonwoven fabric.

[0038] Furthermore, the heat exchange chamber is a plate heat exchanger structure, and the internal circulating medium is flexibly selected according to the in-situ temperature control requirements, preferably heat transfer oil (preferably mineral-based or alkylbenzene-based heat transfer oil) or circulating cooling water. In this embodiment, the heat-conducting partition is selected from 316L stainless steel.

[0039] A method for preparing phosphorus oxychloride based on a flat-plate membrane reactor, wherein the method uses phosphorus trichloride and oxygen as raw materials and carries out an oxidation reaction in a flat-plate membrane reactor, including the following steps: Phosphorus trichloride is continuously introduced into the liquid chamber of the reactor, while oxygen is introduced into the gas chamber to control the reaction temperature and oxygen pressure. Oxygen permeates through the micropores of a porous hydrophobic membrane under pressure, and the micro-interface contact between the gas and liquid phases is achieved through the porous hydrophobic membrane, allowing oxygen to undergo an oxidation reaction with phosphorus trichloride in the form of molecular diffusion to generate phosphorus oxychloride. During the reaction, the heat of reaction is removed in a timely manner through the circulation of the heat exchange medium to maintain a stable reaction temperature; The reaction products are continuously discharged from the liquid chamber outlet.

[0040] Furthermore, the phosphorus trichloride feedstock is continuously pumped from the upstream feed tank into the liquid chamber of the flat-plate membrane reactor via a transfer pump, and the phosphorus oxychloride-rich product generated by the reaction is continuously discharged from the liquid chamber outlet and enters the downstream product collection or purification unit. The entire process is a unidirectional continuous flow.

[0041] Furthermore, the reaction temperature is 70-95℃, preferably 85-95℃.

[0042] Furthermore, the oxygen pressure is controlled within the range of 0.01-0.05 MPa.

[0043] To improve the single-pass conversion rate and system capacity of phosphorus trichloride, multiple reactors are connected in series, with 3 to 5 reactors in total. When multiple reactors are connected in series, the inlet of the liquid chamber of the first-stage reactor is connected to the phosphorus trichloride delivery pipeline, and its outlet is connected to the inlet of the liquid chamber of the second-stage reactor. The outlet of the liquid chamber of the second-stage reactor is then connected to the inlet of the liquid chamber of the tertiary reactor, and so on. Each reactor is equipped with a separate gas and circulating medium supply and treatment system. Example 2

[0044] This embodiment uses a single flat-plate membrane reactor to prepare phosphorus trichloride, and includes the following steps: Phosphorus trichloride was continuously introduced into the liquid chamber of the reactor, while oxygen was introduced into the gas chamber at a pressure of 0.030 MPa. The molar ratio of phosphorus trichloride to oxygen was controlled at 2:1.5, and the reaction temperature was controlled at 85±2℃. Oxygen permeates under pressure through a porous hydrophobic membrane (polytetrafluoroethylene material, 80 nm thick, 0.6 nm pore size, and 2300 m² specific surface area). 2 / m 3 Oxygen permeability is 6 L / min / cm 2 The micropores of the membrane allow for micro-interface contact between the gas and liquid phases through a porous hydrophobic membrane, enabling oxygen to react with phosphorus trichloride via molecular diffusion to generate phosphorus oxychloride. During the reaction, the heat of reaction is removed in a timely manner through the circulation of heat exchange medium (320# heat transfer oil) to maintain a stable reaction temperature; the reaction products are continuously discharged from the liquid chamber outlet.

[0045] In this embodiment, the final product contains 99.3% phosphorus oxychloride and has a residual phosphorus oxychloride content of 0.21%. Example 3

[0046] This embodiment uses three sets of flat-plate membrane reactors to prepare phosphorus trichloride, and includes the following steps: Phosphorus trichloride is continuously introduced into the liquid chamber of the first-stage reactor from the inlet. Simultaneously, oxygen is introduced into the gas chambers of the first-stage, second-stage, and third-stage reactors at a pressure of 0.035 MPa. The molar ratio of phosphorus trichloride to oxygen in the first-stage reactor is controlled at 2:2. The oxygen supply to the second-stage and third-stage reactors is 30%-80% of that in the first-stage reactor. In this embodiment, the oxygen supply to the second-stage and third-stage reactors is 35% and 30% of that in the first-stage reactor, respectively. The reaction temperature is controlled at 90±2℃. Oxygen permeates under pressure through a porous hydrophobic membrane (polytetrafluoroethylene material, 80 nm thick, 0.6 nm pore size, and 2500 m² specific surface area). 2 / m 3 Oxygen permeability is 8 L / min / cm 2The micropores of the membrane allow for micro-interface contact between the gas and liquid phases through a porous hydrophobic membrane, enabling oxygen to react with phosphorus trichloride via molecular diffusion to generate phosphorus oxychloride. During the reaction, heat exchange medium (320# heat transfer oil) is circulated into each stage of the reactor to remove the heat of reaction in a timely manner and maintain a stable reaction temperature; the reaction products are continuously discharged from the liquid chamber outlet of the three-stage reactor.

[0047] In this embodiment, the final product contains 99.4% phosphorus oxychloride and only 0.18% unreacted phosphorus trichloride. Example 4

[0048] This embodiment uses four sets of flat-plate membrane reactors to prepare phosphorus trichloride, and includes the following steps: Phosphorus trichloride is continuously introduced into the liquid chamber of the first-stage reactor from the inlet. Simultaneously, oxygen is introduced into the gas chambers of the first-stage, second-stage, third-stage, and fourth-stage reactors at a pressure of 0.028 MPa. The molar ratio of phosphorus trichloride to oxygen in the first-stage reactor is controlled at 2:1.8. The oxygen supply to the second-stage, third-stage, and fourth-stage reactors is 30%-80% of that in the first-stage reactor. In this embodiment, the oxygen supply to the second-stage, third-stage, and fourth-stage reactors is 36%, 33%, and 30% of that in the first-stage reactor, respectively. The reaction temperature is controlled at 90±2℃. Oxygen permeates under pressure through a porous hydrophobic membrane (made of polytetrafluoroethylene, 80 nm thick, 0.6 nm pore size, and 2400 m² specific surface area). 2 / m 3 Oxygen permeability is 7 L / min / cm 2 The micropores of the membrane allow for micro-interface contact between the gas and liquid phases through a porous hydrophobic membrane, enabling oxygen to react with phosphorus trichloride via molecular diffusion to generate phosphorus oxychloride. During the reaction, heat exchange medium (circulating cooling water) is introduced into each stage of the reactor to circulate and remove the heat of reaction in a timely manner, maintaining a stable reaction temperature; the reaction products are continuously discharged from the liquid chamber outlet of the four-stage reactor.

[0049] In this embodiment, the final product has a phosphorus oxychloride purity of 99.5% and an unreacted phosphorus trichloride content of 0.16%.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flat-plate membrane reactor, characterized in that, It includes a rigid frame and multiple functional units disposed therein, as well as heat exchange units between adjacent functional units; each functional unit is a liquid chamber-gas chamber-liquid chamber formed by a membrane assembly; the heat exchange unit is a heat exchange chamber formed by a thermally conductive partition between adjacent liquid chambers of adjacent functional units or between a liquid chamber and the rigid frame. The diaphragm assembly and the thermally conductive baffle are fixed to the rigid frame by sealing strips to ensure complete isolation of each chamber; The reactor is equipped with end caps at both ends, and the end caps are respectively equipped with a circulating medium inlet, an oxygen inlet, a phosphorus trichloride inlet, a liquid outlet, a gas outlet, and a circulating medium outlet. The circulating medium inlet and the circulating medium outlet are connected to the heat exchange chamber and are respectively connected to the circulating medium supply device and the circulating medium treatment device. The oxygen inlet and the gas outlet are connected to the gas chamber and are connected to the oxygen supply system and the tail gas treatment system. The phosphorus trichloride inlet and the liquid outlet are connected to the liquid chamber and are connected to the phosphorus trichloride conveying pipeline and the product outlet pipeline. The end cap is also provided with a pressure detection port and a temperature detection port, which are connected to a pressure sensor and a temperature sensor, respectively, to detect the reaction pressure and reaction temperature inside the reactor.

2. The flat-plate membrane reactor according to claim 1, characterized in that, The number of functional units is 4-20.

3. The flat-plate membrane reactor according to claim 1, characterized in that, The membrane assembly is composed of a porous hydrophobic membrane and a support layer; the porous hydrophobic membrane has a thickness of 80-200 nm and a pore size of 0.1-1.0 nm; the support layer has a thickness of 100-300 μm and has a porous mesh structure.

4. The flat-plate membrane reactor according to claim 3, characterized in that, The specific surface area of ​​the porous hydrophobic membrane is 1500-3000 m². 2 / m 3 The oxygen permeability is 0.1-10 L / min / cm. 2 .

5. The flat-plate membrane reactor according to claim 3 or 4, characterized in that, The porous hydrophobic membrane is made of a material selected from one or a copolymer of polytetramethylpentene, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene, polysulfone, polyethersulfone, silicone resin, and polydimethylsiloxane; the support layer is made of a material selected from one of polyester nonwoven fabric and polypropylene nonwoven fabric.

6. The flat-plate membrane reactor according to claim 1, characterized in that, The circulating medium in the heat exchange chamber is heat transfer oil or circulating water; the material of the heat transfer baffle is selected from 316 / 316L stainless steel, duplex stainless steel, industrial pure titanium, Hastelloy, Inconel, graphite or silicon carbide ceramic.

7. A method for preparing phosphorus oxychloride using a flat-plate membrane reactor according to any one of claims 1-6, characterized in that, Includes the following steps: Phosphorus trichloride is continuously introduced into the liquid chamber of the reactor, while oxygen is introduced into the gas chamber to control the reaction temperature and oxygen pressure. Oxygen permeates through the micropores of a porous hydrophobic membrane under pressure, and the micro-interface contact between the gas and liquid phases is achieved through the porous hydrophobic membrane, allowing oxygen to undergo an oxidation reaction with phosphorus trichloride in the form of molecular diffusion to generate phosphorus oxychloride. During the reaction, the heat of reaction is removed in a timely manner through the circulation of the heat exchange medium to maintain a stable reaction temperature; the reaction products are continuously discharged from the liquid chamber outlet.

8. The method for preparing phosphorus oxychloride according to claim 7, characterized in that, The reaction temperature is 70-95℃, and the oxygen pressure is controlled within the range of 0.01-0.05 MPa.

9. The method for preparing phosphorus oxychloride according to claim 7, characterized in that, Phosphorus trichloride is prepared by using 3-5 flat-plate membrane reactors in series: the inlet of the liquid chamber of the first-stage reactor is connected to the phosphorus trichloride delivery pipeline, and its liquid chamber outlet is connected to the inlet of the liquid chamber of the second-stage reactor. The liquid chamber outlet of the second-stage reactor is then connected to the inlet of the liquid chamber of the third-stage reactor, and so on. Each stage of the reactor is equipped with a separate gas and circulating medium supply system and treatment system.

10. The method for preparing phosphorus oxychloride according to any one of claims 7-9, characterized in that, The obtained phosphorus oxychloride product has a purity of ≥99.0% and an unreacted phosphorus trichloride content of ≤0.3%.

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